Purpose of the study is to assess if there is any difference in the reaction rate that individuals experience when they are treated with immune globulin intravenous (IGIV) S/D versus a commercially available non-solvent detergent treated IGIV. IGIV has become a mainstay for the treatment of primary humoral immune deficiency disorders and immune thrombocytopenic purpura and is an important adjunct in the treatment of B cell chronic lymphocytic leukemia. Concern over reported instances of post-transfusion hepatitis [largely, if not exclusively, attributed to hepatitis C virus (HCV)] associated with the use of various IGIV preparations has resulted in a modification in the manufacturing process. The modification is designed to add an extra margin of safety. The process involves the exposure of an IgG-rich plasma fraction to a solvent/detergent suspension which inactivates blood borne lipid- enveloped viruses. Studies comparing the Gammagard S/D product with other non solvent/detergent treated, commercially available IGIV preparations have not been done to date.